Death from prostate cancer (PCa) is caused by the metastatic dissemination of PCa cells from the prostate gland. Dietary consumption of genistein is associated with a lower incidence metastatic PCa. In preclinical models genistein inhibits PCa cell motility and metastasis at concentrations linked to dietary consumption. In a prospectively designed clinical trial, genistein exerts antimotility efficacy on prostate cells in man. We hypothesize that genistein therapeutically modulates signaling pathways in man that regulate PCa cell motility. We have elucidated two signaling pathways by which human PCa cells regulate motility: (1) the heat shock protein 27 (HSP27) pro-motility pathway-inhibited by genistein. (2) the endoglin anti-motility pathway-activated by genistein. In animals, genistein inhibits human PCa metastasis. In phase 1 and phase 2 trials in men with PCa, genistein is well tolerated, inhibits prostate cell detachment, and selectively modulates genes which regulate PCa cell motility. We propose three Aims designed to increase our understanding of how PCa cells regulate motility, of how genistein modulates those regulatory pathways, and of genistein's effect in man. Aim 1 Elucidate the mechanisms by which endoglin (a TGF2 superfamily accessory receptor) regulates PCa cell motility, and determine their role in mediating genistein's efficacy. Studies will identify which TGF2 type II receptor subtype is necessary for endoglin signaling. They will also determine whether endoglin mediates cell motility by binding to integrin adhesion molecules. Genistein's dependence upon each of these mechanisms will be evaluated. Aim 2 Determine whether HSP27 inhibits genistein efficacy by modifying actin function. The role of HSP27-actin interaction in regulating cell adhesion and invasion, and genistein efficacy, will be determined. As HSP27 is up regulated during PCa progression in man, murine studies will assess whether HSP27 regulates PCa metastatic behavior, and how its expression affects genistein antimetastatic efficacy. Aim 3 Assess if genistein alters molecular pathways in man which regulate prostate cell motility. Using banked prostate tissue from our phase 2 trial, investigations will determine whether genistein exerts therapeutically relevant anti-motility effects at the molecular level in man. Studies performed upon human tissue will be dictated, in part, by investigations performed in Aims 1 and 2. Prostate cancer causes death by moving throughout the body, thereby forming metastasis. PUBLIC HEALTH RELEVANCE Genistein is a chemical in soy that inhibits metastasis in animals. We have shown that in man, genistein appears to stop prostate cells from moving. This proposal seeks to find out how genistein is working in man. This information is necessary in order be able to use genistein to effectively inhibit prostate cancer metastasis in man.